Today, a comprehensive list of risk factors for physical and psychological morbidity must include a behavioral element that has origins, at least for some individuals, early in development. Early social trauma(s) and challenges(s) affect the developing individual in many ways (e.g., behaviorally and physiologically). As the incidence of HIV infection rises in adolescent populations, particularly those with numerous childhood traumas, an understanding of the impact of these events on viral and disease resistance becomes increasingly more consequential. Separations from mother are significant events that occur frequently during development. The extent to which these separation experiences affect subsequent mother-infant relationships is important in determining etiology of any long term consequences for biobehavioral development. The present project evaluates: 1) changes in the mother-infant relationship subsequent to maternal separation experiences; 2) altered behavioral responses to novel situations that might be related to separation history; 3) long term induction of enhanced lysis tumor targets by periphal blood lymphocytes following a separation experience; 4) changes in patterns of lymphocyte cytokine production and release that contribute to the enhanced natural cytotoxicity, and most importantly; 5) evaluation of relative risk for progression of disease following inoculation with SIVsmE660 based on early development history. The nature of these changes in immune parameters observed after single brief early maternal separation experiences (e.g., enhanced natural cytotoxicity and reduced antibody responses) do not lend themselves to obvious predictions regarding disease risk. These changes can be reconciled with themselves but they potentially predict both enhanced and reduced viral resistance. One approach for resolving this dilemma is an empirical test via direct challenge such as proposed herein. Regardless of outcome, the role of early development is lacking in most models applied to AIDS research, and as such this application seeks to provide that context.